Pyrolysis vs. hydrothermal carbonization: Understanding the effect of biomass structural components and inorganic compounds on the char properties

The influence and role of the different biomass components during HTC and pyrolysis as well as its effects on the char properties were studied. For this, three agricultural residues (wheat straw, pine bark and macauba nut shell) in three different forms (original, leached with acetic acid and synthetic mixtures) were chosen as precursors. Synergies between the biomass components were evidenced: the biomass samples with the higher lignin content lead to higher biochar yields and the biomass samples in general lead to higher yields than the synthetic mixtures. Furthermore, the viscoelastic nature of lignin was overshadowed by the rigidity of cellulose in the real biomass samples leading to thermally more stable biochars with larger surface areas. Leaching the inorganics from the biomass lead to biochars with the largest surface areas and it had a positive impact on the carbon contents and calorific values.